Putative role of epithelial derived factors in airway smooth muscle reactivity

Until recently the contractile actions of asthma mediators have been examined in vitro without consideration of the modulatory role of the associated epithelial cells. Removal of the epithelium in vitro augments contraction and reduces relaxation to several bronchoactive agents and bioassay experiments have shown that the protective effects of the epithelium can be transferred to denuded preparations. It now seems likely that one or more epithelial-associated factors eg EpDRF and PGE2 have a protective role in controlling airway contractility. These findings may be important in asthmatics in vivo since there may be some correlation between epithelial damage/loss and airway hyperreactivity. The identity of EpDRF remains unknown but it does not appear to be a prostanoid and is distinct pharmacologically from EDRF found in blood vessels.